Blender can't open blend file using Append. Says "Listing Dirs..." but does nothing
Sounds like a bad blend file.

You mentioned having purchased it, so I am assuming you downloaded it from some kind of online store, right? Have your tried downloading it again, file might be incomplete or have become somehow corrupted.

Is the file very big, does it contain a lot of images (like say textures for the trees or something) or very big meshes? It might just take a while to load all information.

Can you open the file directly?